49ers rookie Martin suffers knee injury

SANTA CLARA -- Rookie center Marcus Martin became the latest in a string of 49ers to sustain knee injuries in the past month.

Martin's left knee apparently got injured while he blocked on a Glenn Winston run with 11:11 remaining in Sunday's exhibition win over the San Diego Chargers.

Martin's legs got rolled up on at the end of the play, and he had to be carted off the Levi's Stadium's field, though only after a large contingent of teammates lined up to wish him well.

The 49ers have lost four players to season-ending knee injuries since training camp began a month ago: running back Kendall Hunter, guard Fou Fonoti, wideout Chuck Jacobs and linebacker Blake Costanzo.

Martin, a third-round pick out of USC, was hindered by an ankle injury during training camp, virtually eliminating him from contention for the starting center job with Daniel Kilgore.